Since the combustion state of an air-fuel mixture in an internal combustion engine changes depending on the components of the fuel used, the power of the engine also varies depending on the fuel components.
For example, the power of an internal combustion engine that can use a blended fuel obtained by blending a gasoline fuel and an alcohol fuel changes in accordance with the alcohol concentration in the blended fuel. The control apparatus for an internal combustion engine disclosed in Japanese Laid-Open Patent Publication No. 2007-137321 thus estimates the alcohol concentration in a blended fuel, and changes the control state of the engine, such as the fuel injection amount and the ignition timing in accordance with the estimated alcohol concentration.
The alcohol concentration of a blended fuel used in the above internal combustion engine varies in a range from 0% to 100%. Accordingly, on the assumption that a blended fuel containing alcohol fuel of the above concentration range will be used, an estimation program for estimating the alcohol concentration in a blended fuel and a control program for changing the control state of the engine in accordance with the alcohol concentration is developed. Therefore, as long as the alcohol concentration is within an expected range, the engine can be properly controlled in accordance with the alcohol concentration.
Changes in the fuel components include not only changes in the alcohol concentration in a blended fuel, but also changes in the octane number and deterioration of the fuel. In the case where changes in the fuel components will certainly be within expected ranges, programs for detecting the fuel components in accordance with the expected ranges are prepared, so that the influence of compositional differences of fuel on the engine power can be determined.
The above illustrated configuration can be used only in the case where the fuel used in the internal combustion engine is predictable, and the programs are previously given compatible values that correspond to the use of fuels in the expected ranges. However, an unexpected fuel, for example, a newly developed fuel that did not exist when the programs were developed or a fuel that has deteriorated further than when the programs were developed, may possibly be used. In such cases, the use of an unknown fuel cannot be detected. Hence, the influence of compositional differences of fuel on the engine power cannot be accurately detected.
Such insufficient detection of the influence of compositional differences of fuel on the engine power causes the following drawbacks.
For example, in an automatic transmission for an internal combustion engine, hydraulic pressure supplied to hydraulically actuated portions such as the clutch and brake, which are operated when the gear is shifted, is adjusted in accordance with the engine power. More specifically, the input torque transmitted from the engine to the transmission is computed based on the engine power, and the hydraulic pressure supplied to the hydraulically actuated portions is adjusted based on the computed input torque. When the input torque is great, the hydraulic pressure supplied to the hydraulically actuated portions is raised to prevent the hydraulically actuated portions from skidding. When the input torque is small, the hydraulic pressure supplied to the hydraulically actuated portions is lowered so that excessive hydraulic pressure is not supplied. Such hydraulic pressure control improves the fuel consumption and the durability of the automatic transmission. If the influence of compositional differences of fuel on the engine power cannot be accurately detected when the hydraulic pressure control is executed, the accuracy of the estimation of the input torque is lowered. This can lead to excessive or insufficient hydraulic pressure supplied to the hydraulically actuated portions.